ML iterative tentative-decision-directed (ML-ITDD): a carrier synchronization system for short packet turbo coded communication

Abstract

The invention of turbo codes has manifested the ability of communications systems to operate at very low signal to noise ratio, very close to the theoretical Shannon capacity limit. However, synchronization of turbo-coded signals operating in low SNR conditions may be difficult, especially for short packet transmission. This paper proposes the maximum-likelihood iterative-tentative decision-directed (ML-ITTD) circuit for using the tentative decisions produced by the turbo decoder to improve the carrier synchronization in turbo coded short packets communication systems. The ML-ITDD method operates iteratively and jointly with the turbo decoder, enhancing both the turbo-decoder and the synchronization performance. The ML-ITDD method has been shown by simulation to significantly increase the allowed initial frequency and phase uncertainty region, thus allowing the use of very short training sequences for initial carrier synchronization.